Baseline concentration of Cd, Co, Cr, Cu, Pb, Ni and Zn in surface soils of South Africa
THE AIM OF THIS STUDY WAS TO DRAW up baseline concentrations for several environmentally important trace elements in South African soils. A major inventory of some 4500 soil profiles has been compiled in South Africa over the past three decades and information on chemical composition can now readily be generated for the country as a whole. Selected soil samples from surface horizons were analysed by inductively coupled plasma-mass spectrometry for total (nitric acid-extractable; EPA method 3050) and available (NH4EDTA-extractable) fractions of Cd, Co, Cr, Cu, Ni, Pb and Zn. A baseline concentration range (defined as 95% of the expected range of background concentrations) was calculated for each element from geometric means and standard deviations after the data set was normalized by log 10 transformation. These supposedly natural, baseline values were used to revise South African guidelines and to set the total investigation level and the total maximum threshold level in each case as follows: Cd 2 and 3; Co 20 and 50; Cr 80 and 350; Cu 100 and 120; Ni 50 and 150; Pb 56 and 100; and Zn 185 and 200 mg kg-1, respectively. Four-fifths of all soils were found to be Zn-deficient, one-third Cu-deficient and one-fifth Co-deficient.